This invention relates generally to wireless communications, and more particularly to automatic frequency control.
Wireless access provides tetherless access to mobile users, this has been done principally to address the requirements of two specific and disjoint domains: voice telephony and indoor data LANs. Cellular telephone networks have extended the domain of telephone service over a wireless last hop, while mobile-IP LANs such as WaveLAN and RangeLAN do the same for indoor users of TCP/IP data networks. Advances with wireless technology and high-speed integrated service wired networking promises to provide mobile users with comprehensive multimedia information access in the near future.
Personal Communication Services (PCS) are a broad range of individualized telecommunication services which enable individuals or devices to communicate irrespective of where they are at anytime. Personal Communication Networks (PCN) are a new type of wireless telephone system communicating via low-power antennas. PCNs offer a digital wireless alternative to the traditional wired line.
As a cellular mobile radio moves from one cell to another, it is xe2x80x9chandedxe2x80x9d off to the next cell by a controller, which determines which cell is receiving the strongest signal. Because the cellular user remains closer to the base transceiver than in classical mobile communications, the cellular user""s transceiver requires less power and is therefore less expensive. The great advantage of the cellular concept over non-cellular radio is that higher capacity is allowed with the same frequency allocation. This advantage comes at a cost, the necessity of a large number of cell sites and associated radio ports.
Cellular and PCS technologies that are based on Time Division Multiple Access (TDMA) and Frequency Division Multiple Access (FDMA) require accurate control of the carrier frequency. Typical cellular base stations use a 0.2 ppm tolerance carrier frequency crystal and mobile units use 2.5 ppm tolerance carrier frequency crystals. In a cellular base station the tighter tolerance is achieved through higher costs and larger size. The design of a PCS system requires smaller cells and subsequently more Personal Base Stations (PBS).
Therefore, there is a need for maintaining tight tolerance of carrier frequency at a lower cost.
In accordance with the present invention, there is provided in a wireless communication network having public frequency channels, a method for automatic frequency control for a cellular base station. The method comprising the steps of: scanning the public frequency channels; locking the cellular base station to a signal on one of the public frequency channels; and returning the cellular base station to normal operation.